Novel screening strategy can lead to microorganism-based crop protection methods

Certain nonpathogenic microbes can trigger the immune responses of plants without damaging them, allowing these pathogens to behave similarly to plant vaccines. However, screening these microbes for these properties has historically been costly and time-intensive.

The novel screening method can help scientists identify microorganisms that stimulate plant immune mechanisms without harming the plants themselves. Video Credit: Tokyo University of Science.

A research team from the Tokyo University of Science has now designed a new screening technique based on cultured plant cells that render such testing relatively easier. This strategy may result in microorganism-based crop protection techniques that minimize the requirement for chemical pesticides.

Unique immunity mechanisms have been evolved by plants which they can trigger upon identifying the presence of a pathogen. Fascinatingly, the presence of certain nonpathogenic microbes can also trigger a plant to stimulate its systemic immunity mechanisms, and a few research works have demonstrated that pretreating agricultural crops with these “immunity-activating” nonpathogenic microbes can make the crops more prepared to combat infections from pathogenic microbes.

This actually implies that immunity-activating nonpathogenic microbes can work similar to plant vaccines, offering a low-risk stimulus for the immune system of the plant that prepares the latter to deal with real threats.

These are interesting discoveries for crop scientists because they indicate the viability of utilizing this pretreatment as a kind of biological pest control that would decrease the requirement for agricultural pesticides.

But before pretreatment with nonpathogenic microbes turns out to be a routine agricultural technology, investigators require a means to screen microbes for the potential to trigger the immune systems of the plants without harming them.

At present, there is no easy technique to assess the potential of microbes to stimulate the plant immune systems. Traditional techniques involve the application of whole plants and microbes, and this naturally makes conventional screening a costly and time-intensive method.

To overcome this issue, Associate Professor Toshiki Furuya and Professor Kazuyuki Kuchitsu from the Tokyo University of Science and their collaborators decided to devise a new screening method that involves cultured plant cells. An explanation of the researchers’ technique was recently provided in the Scientific Reports journal.

In this screening method, the first step is to incubate the candidate microorganism along with BY-2 cells, which are tobacco plant cells popular for their stable and quick growth rates. The second step is to treat the BY-2 cells with cryptogein—a type of protein released by fungus-like pathogenic microbes that can trigger immune reactions from tobacco plants.

A major portion of the cryptogein-induced immune responses is the development of a group of chemicals, known as reactive oxygen species (ROS). Investigators can easily quantify the cryptogein-induced ROS production and apply it as a metric to assess the impacts of the nonpathogenic microbes.

In other words, an effective pretreatment agent will boost the ROS production levels of the BY-2 cells (that is, it causes the cells to show a more robust immune system activation) in reaction to cryptogein exposure.

To test the feasibility of their new screening method, Dr. Furuya and his collaborators applied the method to 29 strains of bacteria extracted from the inside of the Japanese mustard spinach plant (Brassica rapa var. perviridis), and they observed that eight strains increased the cryptogein-induced ROS production.

The team subsequently tested these eight strains by applying them to the root ends of seedlings from the Arabidopsis genus, containing species often used as model organisms for plant biology studies. Fascinatingly, two of the eight tested strains triggered whole-plant resistance to bacterial pathogens.

Based on the proof-of-concept results regarding those two bacterial strains, Dr. Furuya happily noted that the screening method developed by his team “can streamline the acquisition of microorganisms that activate the immune system of plants.”

When Dr. Furuya was asked how he visualizes the screening strategy impacting agricultural practices, he explained that he anticipates his group’s screening system “to be a technology that contributes to the practical application and spread of microbial alternatives to chemical pesticides.”

In due time, the new screening technique devised by Dr. Furuya and the research group may make it considerably easier for crop scientists to produce greener agricultural techniques that depend on the defense mechanisms evolved by plants over millions of years.